The hypotheses to be tested in these intraoperative studies are: a) true obstruction to left ventricular outflow due to mechanical impedance exists in patients with hypertrophic cardiomyopathy (HCM) who have a subaortic pressure gradient and b) operative intervention to relieve this obstruction results in relief of the obstruction and elevated intraventricular systolic pressures, which are detrimental to left ventricular performance. Solid state pressure transducers, electromagnetic flow transducers, and a Hewlett-Packard ultrasonic system will be applied under direct exposure intraoperatively in consecutive obstructive HCM patients undergoing first-time operative intervention. Echocardiographic studies preoperatively, intraoperatively (pre-and post-procedure), and postoperatively will include 2-dimensional (2-D), M-mode, and color Doppler imaging, in addition to pulsed Doppler, and continuous wave Doppler (CWD). The intraoperative echocardiography will be obtained simultaneous with hemodynamic measurements of left ventricular outflow tract (LVOT) pressure gradient and aortic blood flow. The findings of this study are expected to provide evidence supporting the presence of true mechanical obstruction of the LVOT in patients with HCM. These data should support the increased use of surgical palliation in selected patients.